1. Field of the Invention
The present invention relates to a method of and an apparatus for compressing a digital video signal, and more particularly, to a method of and an apparatus for coding a zerotree wavelet image based on a zero tree wavelet transform.
2. Description of Related Art
Image transmission and storage are important for Internet and multimedia services. However, since image transmission and storage systems have limited bandwidths and memories, image coding is important to the efficiency, speed, and costs of image transmission and storage systems.
Image coding standard H.263 shows reliable coding efficiency. The moving picture experts group (MPEG)-4 and joint photographic experts group (JPEG)-2000 have also introduced various coding techniques for improved coding efficiency.
In particular, in the MPEG-4 and the JPEG-2000, to achieve coding efficiency, wavelet transforms have been considered as a replacement for existing discrete cosine transforms (DCT).
In MPEG-4, coding employing the wavelet transform (hereinafter, referred to as wavelet coding) has been used in texture coding to achieve scalability. Also, in the JPEG-2000, the wavelet coding is used to maximize the coding efficiency by preventing images of various sizes, particularly, very large images, from being blocked. Blocking refers to artificial frontiers in images coding by discrete cosine transforms, such as MPEG-4 and H.263.
Embedded Zerotree Wavelet (EZW) coding (J. M. Shapiro) and Set Partitioning in Hierarchical Trees (SPIHT) coding (A. Said and W. A. Pearlman) are efficient image coding techniques that attempt to eliminate blocking.
These coding techniques can organize a plurality of wavelet coefficients into one symbol, i.e., a zerotree, using a spatial location and orientation of a wavelet coefficient shown in FIG. 1 to improve compression efficiency.
However, in general, MPEG-4 and JPEG-2000 systems, which are based on a discrete wavelet transform, are limited and the number of wavelet decompositions is fixed. Thus, when the size of an image varies, or the number of wavelet decompositions varies depending on the characteristics of the image, the coding efficiencies of the MPEG-4 and JPEG-2000 systems are compromised.
Therefore, a need exists for a method and apparatus for coding a grouped zerotree wavelet image having high coding efficiency irrespective of the scale of a wavelet transform.